Electro-optic reader for retro-reflective bar codes

ABSTRACT

A system for identification comprising: a surface ( 14 ) comprising retro-reflective indicta; a source of light that illuminates the indicta ( 18 ) along an illumination direction; and a detector ( 20, 21 ) that views light reflected from the indicta, wherein the retro-reflector reflects the light that illuminates it as a plurality of beams at a plurality of angles relative to the illumination direction.

FIELD OF THE INVENTION

[0001] The invention relates to the field of electro-optic readers andcards and in particular to readers, cards labels or other markedsurfaces and algorithms suitable for electro-optic reading of cardslabels or other marked surfaces at relatively long distances.

BACKGROUND OF THE INVENTION

[0002] Optical Remote reading of cards, for example for identification,is well known. In general, such cards contain a bar code, such as a code39, which is read by a remote scanner. Reading at distances of severalfeet is possible but not easy in many applications. In general, cardscontaining a bar code are placed in a side window of a vehicle and ascanner placed at the side of a road on which the vehicle travels areused to identify cars, for example at a gate. Since the position of thecards can be controlled (the card is placed at a height at which italways can be read) and the aspect of the card is almost normal to thescanner, such reading can be fairly successful.

[0003] The prior art does not read cards placed in the front window of acar, for at least four reasons. One reason is that the position, tiltand aspect (angle of incident light with respect to normal) of the cardare less controllable. The second reason is that the use of a laserscanner that points at a drivers eyes, even one in the infrared, is notconsidered safe. A third reason is that such scanners, especially formeasurement at a distance, are expensive. A fourth reason is that thereare often stickers or other devices on the windshield of a vehicle,which may be mistaken by a reader for the card to be read.

[0004] Flat Retro-reflective sheets are well known. Such reflectors maybe of the type utilizing arrays of micro-elements, such as cornerreflectors or of the type using beads or other cats-eye type structuresto return the light. In general, the acceptance angle (the range ofincident angles at which incoming light is retro-reflected) is dependenton the retro-reflector type used. Retro-reflectors are generallyimperfect and have a, generally small, spread of angles around the retroangle at which the light is reflected.

[0005] Labels utilizing retro-reflector enhanced indicta have been usedfor providing improved readability of the indicta, for example ofindicta placed over them. When the indicta are illuminated, theretro-reflectors selectively reflect the light in the direction of thelight source, thereby providing a bright background for the indicta andincreased contrast. The prior art also shows the use of colored indictaand the generation of retro-reflector enhanced indicta generated byproviding areas of retro-reflectors in the form of an image that isretro-reflected. The indicta/retro-reflectors may be overlayed by otherindicta (holograms and engraved patterns are suggested in the art),and/or by coatings that reflect or absorb light at certain wavelengths.

[0006] Directed reflectors are also known. A directed reflector is areflector that reflects incident light at an angle that is offset by afixed amount from the angle of incidence. One method of generatingdirected reflectors is by utilizing corner reflectors with faces thatare not perpendicular. Reference is made in this regard to “Study ofLight Deviation Errors in Triple Mirrors and Tetrahedral Prisms”,Yonder, J., JOSA, V. 48 (7) 1958.

SUMMARY OF THE INVENTION

[0007] A broad aspect of some embodiments of the invention is concernedwith a remote card reading system.

[0008] In some embodiments of the invention, a card or other surfacehaving retro-reflecting enhanced indicta, such as a card marked withindicta overlaying a retro-reflector, is used. In an embodiment of theinvention, the retro-reflector reflects the light in directions around acentral axis equal to the incident axis of the light. However, the lightis reflected in a cone-like cross-section in which the intensity oflight reflected along the axis is lower than the intensity reflected atsome (peak) design angle α from the axis. The term “circular offsetangle” is used herein for the angle α.

[0009] In some embodiments of the invention, a camera views the card.The card is placed at a distance from the source and camera such thatthe camera views a retro-reflection enhanced image of the indicta at thecircular offset angle α. In this situation, the orientation of the cardis not critical, within the acceptance angle of the retro-reflector,since the high intensity lobe of the reflection is at the same angle,independent of the orientation of the retro-reflected indicta.Optionally, a second camera is placed at an angle at which theretro-reflection is small. This allows for the screening and rejectionof cards that do not have the indicated angular deviation ofretro-reflection. Alternatively or additionally, a first image isacquired by the camera at a first distance at which the camera should beable to acquire a retro-reflected image. A second image is acquired at acloser distance at which the retro-reflected light should be absent.Only cards that give an image at the proper distance are verified. Thedistance may be measured directly, as by a 3D camera or range finder, orindirectly, as by a presence sensor in the road for a vehicle thatcarries the card. Alternatively or additionally, the card may be fittedwith two or more types of retro-reflectors, each having a differentoffset angle. Strategically placed cameras or acquisition distances canprovide the same safety features described above.

[0010] In some embodiments of the invention further security may beadded by utilizing one or more of (1) analysis of a diffraction patternof the retro-reflectors, (2) providing different retro-reflectivecontrast over portions of the card, (3) optical coatings that causespectrum differences for various portions of the card, (4) detection ofa reflection pattern of the retro-reflector or (5) asymmetricalretro-reflectance. Other security measures, known in the field of creditand identification cards can also be used.

[0011] It is a feature, of some embodiments of the invention, that barcodes can be read at distances of 8, 10, 12 or more meters utilizing aCCD camera and incoherent pulsed (or continuous) IR (or visible)illumination, day or night.

[0012] An aspect of the invention is concerned with the design of a cardor other surface for identification or recognition purposes.

[0013] In an embodiment of the invention, the card comprisesretro-reflection enhanced indicta. These indicta can be formed byproviding indicta over a retro-reflecting surface. Alternatively oradditionally, only a portion of the surface may be provided with aretro-reflective surface, such that the retro-reflected light forms animage. Alternatively or additionally, the contrast between differentportions of the image may be varied, as for example by coating a portionwith a partially absorbing surface or by providing retro-reflectiveelements having different efficiencies over various portions of thesurface or by damaging portions of the retro-reflective element.Alternatively, only portions of the retro-reflector indentations arecoated to alter their reflectivity. In an embodiment of the invention, afirst set of indicta (for example a bar code) is formed over aretro-reflecting surface. The retro-reflecting surface is divided intovarious sections that have different retro-reflectivities. Thesesections may form a pattern that provides an additional form or securityconfirmation.

[0014] In some embodiments of the invention, the indicta on the card areof the form described below with respect to an optional optimized codeof the invention.

[0015] In some embodiments of the invention, the card is provided with aprinted layer containing the normal identification information that onefinds on credit cards or passes. The retro-reflective indicta are underthis layer. The printed layer is preferably substantially transparent tothe light used to interrogate the retro-reflective indicta.

[0016] An aspect of the invention is concerned with the design of a barcode especially suitable for use with remote reading by a camera andwith a methodology of reading bar codes, especially suited for readingsaid codes at a distance by imaging of the bar code.

[0017] As a preliminary matter, it should be noted that for capture ofbar code information from a card, placed, for example, in the windshieldof an automobile, an image of a large area is captured. For a standard780×580 CCD detector, if 8 code 39 characters are utilized, in a stackedconfiguration, on a standard credit card size substrate, the narrowelements in the bar code will be between 2 and 3 pixels wide, whenacquired at 8-12 meters. Since the card forms only a relatively smallpart of the acquired image, it is preferable to identify the card on theimage and perform image processing only on the portion of the imagecontaining the card. It is also possible that the card may be upsidedown or sideways. Under field conditions it is possible that part of thesubstrate may be obscured. However, cards can be decoded even when thedistance is as large as 20 meters. It is understood that the use ofhigher resolution cameras such as 1024×1024 or 2048×2048 cameras gives ahigher resolution and can result in a higher range of detection.

[0018] In the standard code 39 bar code, the number of differentcharacters is limited to 43 specific variations of the bar combinations.This limitation is imposed to reduce the ambiguity between similarcharacter configurations. In some embodiments of the invention anextended variant of the “code 39” bar code is used. In this extension,the number of characters is higher than the normal number. For example,for the code 39 structure, 84 combinations are possible and may be used.For access cards, for which the number of required codes is not high, itmay be more desirable to have redundancy rather than total lack ofambiguity. For example if six characters are available, use of thestandard 39 bar code, with 43 variations give (43)⁶=6.3 billioncombinations. The use of the variant bar code using a full number ofpossible combinations with triple redundancy gives (84)²=7056combinations. For double redundancy, the number of combinations is(84)³=592,704. Although the number of variations is lower for theredundant methodology, the redundant scheme is sometimes more desirableunder remote reading conditions, since there is a distinct possibilitythat one or more of the characters may be covered or otherwiseunreadable. Furthermore, for a moving vehicle, the system may only beable to acquire a limited number of images while the card is in range.In some embodiments of the invention, deblurring algorithms, as known inthe art, may be used.

[0019] In some embodiments of the invention, the code is formed as aseries of stacked rows of characters. In order to allow for at least a 2pixel width for a narrow line element, the number of characters per row(on a card) is limited to two characters, when the row is parallel tothe long side of the card. From signal to noise and size considerations,the total number of rows is sometimes limited to 4 or 5, resulting in 8characters per card (for 4 rows). Since account must be taken of theconditions under which the card is read, it generally preferred toprovide a check-sum character and preferably two check sum characters.This allows for 6 data characters, with either two (three characters) orthree (two characters) fold redundancy. If all eight characters are usedfor data, the possibilities are two (four characters) or four (twocharacters) fold redundancy. Other codes, may be used in someembodiments of the invention.

[0020] Another type of redundancy which may be utilized is having thesecond appearance of the code not be an exact copy of the firstappearance of the code. Each of the characters in the second appearanceof the code may be a function of two or more characters in the originalcode. Other redundancy schemes, known in the art, may also be used.

[0021] In standard code 39 bar code systems, a special character is usedto indicate the start and end of a row or other grouping of charactersor a row. Since, for long distance viewing, the elements of thecharacters must be larger than for near viewing, the number ofcharacters available per unit area is severely reduced. The use of twocharacters out of 8 to indicate start and stop would be very wasteful.Nevertheless, it is necessary to indicate the start of the characterstring and the orientation (up, down or rotated) of the card on theimage.

[0022] In some embodiments of the invention, the card, or the areacontaining the indicta, is formed with a highly reflecting edge. Sincethe card is rectangular, the provision of such an edge allows for thedetermination of orientation of the card. Additionally, in someembodiments of the invention, a black (non-retro-reflecting) border isplaced around the outside of the reflecting border. This allows forbetter visualization of the border. In some embodiments of theinvention, a determination of the size of the border is made. Thisallows for a first order size determination of the expected size of wideand narrow lines and may make the differentiation between them easier.

[0023] In some embodiments of the invention, where stacked bar codes (atleast three) are used the spacing between the rows is different so thatthe top row can be distinguished from the bottom row. Either one of thespaces between the end and an interior row or one of the end rows andthe border (works even with only two rows) or between two of theinterior (but not the middle) rows can be made different from the widthof the other corresponding space. Alternatively, the spacing betweencharacters can be different between the top and bottom rows, with ashort space being used in one and a long space in the other.

[0024] An aspect of some embodiments of the invention is concerned withauthentication methods. Some of these methods are useful for short rangeinterrogation of the cards.

[0025] In accordance with some embodiments, a retro-reflecting surfaceis illuminated by a light source. A detector views the reflected lightfrom the direction of incidence of light from the source. An image,corresponding to the reflections from the retro-reflector, is formed onthe detector. In some embodiments a laser source is used. In others aLED or other incoherent source is used.

[0026] There is thus provided, in accordance with an embodiment of theinvention, a system for identification comprising:

[0027] a surface comprising retro-reflective indicta;

[0028] a source of light that illuminates the indicta along anillumination direction; and

[0029] a detector that views light reflected from the indicta,

[0030] wherein the retro-reflector reflects the light that illuminatesit as a plurality of beams at a plurality of angles relative to theillumination direction.

[0031] Optionally, where the plurality of beams are produced in pairs,the members of the pair lie in a plane and make the same angle with theincident direction, with an opposite sign. Optionally, the plurality ofbeams lie on the surface of a circular cone. Optionally, the pluralityof beams lie on the surface of an elliptical cone. Optionally, theplurality of beams provide a substantially continuous ring of reflectedlight. Optionally, the ring of light has substantially of the sameintensity along its length.

[0032] In an embodiment of the invention, the source and detectorilluminate and view the surface at angles having a differencesubstantially equal to at least one of the multiple reflection angles.Optionally, the system includes at least one additional detector thatviews the surface at an angle substantially different from any of saidmultiple angles.

[0033] Optionally, the plurality of beams define the surface of two ormore circular cones. Optionally, the plurality of beams lie on thesurface of an elliptical cone. Optionally the plurality of beams providea plurality of substantially continuous rings of reflected light.Optionally, each of the rings of light has substantially of the sameintensity along its length.

[0034] In an embodiment of the invention, the source and detectorilluminate and view the surface at angles having a differencesubstantially equal to at least one of the multiple reflection angles.Optionally, the system includes an additional detector said detector andsaid additional detector viewing said surface at an angle substantiallyequal to another of the multiple angles.

[0035] Optionally, the detector is an imaging detector, that forms animage of the light retro-reflected from the surface. Optionally thesystem includes an image processor that receives images formed on thedetector. Optionally, the source of light does not scan the surface.

[0036] In an embodiment of the invention, the imaging detector images afield of view that has an area at least 5, 10, 20, 50 or 100 times aslarge as the area of the surface.

[0037] In an embodiment of the invention, the system includes imageprocessing circuitry that detects the presence of the surface in animage acquired by the imaging detector.

[0038] In an embodiment of the invention, the retro-reflecting surfacereflects light that forms an information carrying image and wherein theimage processing circuitry is operative to extract the information fromthe image. Optionally, the information comprises a bar code. Optionally,the information comprises a two dimensional code. Optionally, theinformation comprises spectral information.

[0039] In an embodiment of the invention, the source of lightilluminates the surface with incoherent light.

[0040] In an embodiment of the invention, the source and detectorilluminate and view the surface at substantially the same angle.Optionally, the detector is an imaging detector. Optionally, the imageon the imaging detector comprises a pattern corresponding to the anglesat which the light is reflected.

[0041] In an embodiment of the invention, the system includesauthentication circuitry which authenticates the surface when thedetector detects a predetermined pattern of light.

[0042] Optionally, the system includes a reflector that reflects thelight reflected by the retro-reflector so that it can be viewed outsidethe path of illumination. Optionally the light source is an incoherentsource. Optionally, the detector is situated at the plane of the sourceor at a virtual plane of the source or at an image of said source planeor virtual source plane.

[0043] Optionally, the light source produces a collimated beam of light.Optionally, the light source is a laser. Optionally, the detector viewsthe light reflected by the retro-reflector without any focusing of thereflected light. Optionally, the system includes a focusing element,having a focal length, that receives the light reflected by theretro-reflector, wherein the detector is placed in the path of the thusreflected beam, spaced from the focusing element by a distance otherthan the focal length.

[0044] Optionally, the retro-reflecting surface is the surface of arelatively inflexible object. Alternatively, the surface is the surfaceof a flexible object. Optionally, the surface is the surface of a card.Optionally, the card has the size of a standard sized credit or smartcard. Optionally, the object is a sticker.

[0045] There is further provided, in accordance with an embodiment ofthe invention a retro-reflective surface having information encodedthereon by having different areas thereof retro-reflecting withdifferent retro-reflective intensities, to form indicta carrying theinformation, wherein the retro-reflector reflects the light thatilluminates it as a plurality of beams at a plurality of angles to theillumination direction.

[0046] Optionally, the plurality of beams lie on the surface of acircular cone. Optionally, the plurality of beams lie on the surface ofan elliptical cone. Optionally, the plurality of beams provide asubstantially continuous ring of reflected light when illuminated by abeam of light. Optionally, the ring of light is substantially of thesame intensity along its length.

[0047] In an embodiment of the invention, the plurality of beams areproduced in pairs, the members of the pair lie in a plane and make thesame angle with the incident direction, with an opposite sign.

[0048] In an embodiment of the invention, the indicta are situated in aninformation carrying portion of the surface and the information carryingportion is surrounded by a retro-reflecting border. Optionally, theretro-reflecting border is surrounded by a non-retro-reflecting border.Optionally, the the non-retro-reflecting border is surrounded by asecond retro-reflecting border.

[0049] Optionally, the information is comprised in a two-dimensionalcode. Optionally, the information is comprised in a bar code.Optionally, the bar code is a code 39 type code. Optionally, the barcode comprises a modified code in which more than 43 characters areavailable. Optionally, 84 characters are available. Optionally, at leastsome of the information appears more than once.

[0050] In an embodiment of the invention, the surface includes marlingsindicating the orientation of the surface. Optionally, the orientationis indicated by the layout of the information carrying indicta.

[0051] In an embodiment of the invention, the said varying intensity ofretro-reflection comprise of a retro-reflecting portion and anon-retro-reflecting portion.

[0052] Optionally, the plurality of beams define the surface of two ormore circular cones. Optionally, the plurality of beams lie on thesurface of an elliptical cone. Optionally, the plurality of beamsprovide a substantially continuous ring of reflected light. Optionally,the rings of light has substantially of the same intensity along itslength.

[0053] Optionally, the retro-reflecting surface is the surface of arelatively inflexible object. Optionally, the surface is the surface ofa flexible object. Optionally, the surface surface of a card.Optionally, the card has the size of a standard sized credit or smartcard. Optionally, the object is a sticker.

[0054] There is further provided, in accordance with an embodiment ofthe invention, a method of reading a bar code comprising:

[0055] forming an image of a bar code with a camera from a distance ofmore than 10 meters; and

[0056] determining the symbols represented by the bar code.

[0057] Optionally, the bar code is comprised in a retro-reflected imageand including illuminating the bar code with light from a controlablelight source.

[0058] Optionally, the retro-reflected image is reflected with a offsetangle relative to the angle of incidence of the illumination from thelight source. Optionally, the distance is more than 15, 20 or 25 meters.

[0059] In an embodiment of the invention, the bar code is formed on acredit card sized substrate. Optionally, the bar code includes at least8 symbols.

BRIEF DESCRIPTION OF FIGURES

[0060] Exemplary, non-limiting embodiments of the invention aredescribed in the following description, read in with reference to thefigures attached hereto. In the figures, identical and similarstructures, elements or parts thereof that appear in more than onefigure are generally labeled with the same or similar references in thefigures in which they appear. Dimensions of components and featuresshown in the figures are chosen primarily for convenience and clarity ofpresentation and are not necessarily to scale. The attached figures are:

[0061]FIG. 1 is a schematic overview of an exemplary system for vehicleidentification, in accordance with an embodiment of the invention;

[0062]FIG. 2 is a schematic block diagram of an interrogation system, inaccordance with an embodiment of the invention;

[0063]FIG. 3 is a schematic illustration of a card, in accordance withan embodiment of the invention;

[0064]FIG. 4 is a schematic illustration of an interrogation system;

[0065]FIG. 5 shows a retro-reflection scheme, especially useful forcarrying out the invention;

[0066]FIG. 6A is graph showing typical retro-reflection profiles ofvarious designs of retro-reflectors;

[0067]FIG. 6B is a schematic illustration of an interrogating system asused in an embodiment of the invention;

[0068]FIG. 7 shows various position/orientation/identification marks, inaccordance with exemplary embodiments of the invention;

[0069]FIG. 8 shows a card layout in accordance with an embodiment of theinvention;

[0070]FIG. 9A is a schematic overview of an alternative exemplary systemfor secure vehicle identification, in accordance with an embodiment ofthe invention;

[0071]FIG. 9B is a schematic drawing illustrating an exemplary layoutfor multiple cameras, in accordance with an embodiment of the invention;

[0072]FIGS. 10A-10D show various authentication schemes, in accordancewith embodiments of the invention;

[0073]FIG. 11 shows a general block diagram of a method for extractinginformation from the indicta on a card, in accordance with an exemplaryembodiment of the invention;

[0074]FIG. 12 is a block diagram showing some detail of a preprocessingalgorithm, in accordance with an exemplary embodiment of the invention;

[0075]FIG. 13 shows a breakdown of the acts involved in an exemplarymethod for detecting the presence and position of a retro-reflectingcard in the image, in accordance with an embodiment of the invention;

[0076]FIG. 14 is a summary flow chart of an exemplary algorithm for thereading a bar code on a card, in accordance with an embodiment of theinvention;

[0077]FIG. 15 is amore detailed flow chart of pre-processing of theimage, in accordance with an exemplary embodiment of the invention;

[0078]FIG. 16 is a flow chart of an exemplary method of reading of thebar code, in accordance with an embodiment of the invention;

[0079]FIG. 17 is a schematic layout of an alternative system for vehicleidentification, according to an embodiment of the invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0080] Overview of the System

[0081]FIG. 1 shows an overview of an exemplary vehicle identificationsystem 10, in accordance with an exemplary embodiment of the invention.As shown, the system has two major subsystems, namely, an interrogatingsystem 12 and an identification card 14. As a result of interrogatingidentification card 14, interrogating system 12 may cause a gate 16 toopen or some other action to be performed.

[0082] Before going on to the details of identification card 14 it isworthwhile to review the major parts of interrogating system 12, shownin FIG. 2. Interrogating system 12 includes, in many of its embodiments,an illuminator 18, a camera 20, a controller 22 and a computer/imageprocessor 24. In some embodiments, computer/image processor 24 may becombined with controller 22 and/or camera 20, into a single unit. Thefunctions described below with respect to computer image processor 24and controller 22 may reside in at least in part in software, firmwareor hardware, which may be dedicated hardware or a programmed generalpurpose computer or controller.

[0083] In operation, illuminator 18 produces light, which illuminates avehicle (or other object) containing card 14 or any other surface havingthe information to be interrogated. Light reflected from card 14 isacquired by camera 20 and passed to computer/image processor 24 forprocessing to determine the information contained on the card. Thisinformation is passed to controller 22, which send a signal to operategate 16 or to perform such other act as may be appropriate.

[0084] In an embodiment of the invention pulsed infrared (IR) light isproduced by illuminator 18 and controller 22 controls and synchronizesthe light production, shutter control of camera 20 and frame grabbing bycomputer image processor 24 to acquire the image produced by the flash.In an embodiment of the invention, the light is non-coherent, forincreased safety. Alternatively, the lighting is continuous andshuttering is provided only by the camera.

[0085] Structure of an Exemplary Identification Card

[0086]FIG. 3 shows a very schematic version of a card 14, in accordancewith an exemplary embodiment of the invention. In particular, card 14,as shown includes a base on which a retro-reflector 26 is formed, anindicta layer 28 and an optional overlay 30 overlaying the indictalayer. Retro-reflector 26 and indicta layer 28 together formretro-reflective indicta 32. It should be understood thatretro-reflective indicta for use in the present invention can be formedin other ways, including without limitation, the formation of a patternof retro-reflective areas separated by non-retro-reflective areas(optionally painted black). Furthermore, the retro-reflectors may be inthe triangular configuration (which gives an efficiency of 66%reflection) or in a hexagonal configuration (which gives a 100%theoretical reflection). Both triangular and hexagonal configurationsare known in the art. Preferably, the surfaces of the corners are coatedto increase their reflection (for open air cube cornerretro-reflectors).

[0087] In an embodiment of the invention, the retro-reflector is theback of a solid optical element in which a front, flat side is viewed.The back side is then coated with a reflector to form theretro-reflector. This provides for a retro-reflector having a higheracceptance angle. Alternatively or additionally, the indicta may beembedded in the optical element or formed in the reflectors to make theindicta more temper-proof.

[0088] In accordance with an embodiment of the invention, optionaloverlay 30 (and any information printed or otherwise formed on it) istransparent to the light produced by illuminator 18. Additionally,overlay 30 may be opaque to visible light (utilizing filters or othermethods known in the art) so that the indicta can not be seen or readwithout proper illumination and instrumentation. Overlay 30 may beprinted, for example, with identification information, with an image ofthe holder, with a hologram, with a magnetic stripe (although such astripe is more conveniently placed on the back-not retro-reflective-sideof the card) or with tamper resisting indicators, other securitymeasurer or other indicta as are known in the art of identificationcards.

[0089] In accordance with some embodiments of the invention, theretro-reflectors are configured such that the peak reflection is notdirectly in the direction of the incoming light. In some embodiments,the reflection peaks at a direction that is a substantially constant andsmall angle offset from the incident light direction. In accordance withan embodiment of the invention, the directions of peak reflection formthe surface of a cone with a small apex angle having an axis along thedirection of light incidence. Generally, the divergence spread aroundthe circular offset angle is small.

[0090] In most commonly used retro-reflectors, the reflection is notcompletely in the direction of incidence. Rather there is somedivergence of the reflection in the form of a profile. FIG. 4 shows theuse of a standard retro-reflector material in the manner of FIG. 2.Source 18 is incident along a line 36 on a retro-reflector 34 at anaspect angle β. Camera 20 is placed a small distance from the source(exaggerated for clarity), such that the angle between the incidentdirection 36 and a view direction 38 of camera 20 is α. It is clear thatfor a high concentration retro-reflector, the beam is much attenuated atthe camera, if it is placed at a view direction much greater than thedivergence of the retro-reflector. On the other hand, if a highdivergence retro-reflector is used, the energy reaching the camera atany position is low. Thus, in order to receive a reasonable intensityimage at camera 20, high interrogating light intensity must be used.

[0091] In accordance with an embodiment of the invention, as shown inFIG. 5, retro-reflector 26 is formed with a specific deviation toproduce a plurality of beams that are reflected at a circular offsetangle along the sides of a cone. FIG. 5 shows a system in which sixbeams are reflected, with a deviation θ from the incident direction 36.The deviation of the reflected beams is small, but is preferably madelarge enough such that the intensity along the peak intensity line 40 issubstantially constant.

[0092]FIG. 6A shows the angular intensity profile of three types ofretro-reflectors. Line 41 is the reflection profile for a typicalcommercial cube-corner reflector. As shown, this device has a full widthhalf maximum divergence angle of about 0.3°. Line 42 is the reflectionprofile for a typical bead-type retro-reflector (for example as used ina license plate). This shows a much higher divergence angle (about 0.8°,total). Commensurate with the wider divergence angle, the intensity inany direction is much lower. Line 43 shows a retro-reflector for use inthe some embodiments of the present invention in which the peak of thereflection for each of the six reflected beams is at an angle of about0.32°. The deviation about this angle is approximately the same as thatfor the commercial retro-reflector shown in the graph. Thisconfiguration gives approximately constant intensity at a deviationangle of 0.32°.

[0093] One way to achieve this conical profile, is to have the cornerangles deviate slightly from 90°. The deviation (for small deviationangles) is approximately {fraction (1/3)} the desired angular deviationfor open air cubes. As seen in the graph, provision of a conicalreflectance profile increases the intensity of light for a camera placedat the deviation angle of 0.32°.

[0094] As indicated, the provision of a substantially conical shape forthe cross-section of the reflection profile results in a system in whichthe reflection to camera 20 is substantially independent of the aspector tilt of the card with respect to the light source/camera. The extentof the incident angle which produces retro-reflection of the typedescribed is, of course, limited. In order to increase this angle, thedepressions forming the corner reflectors may be filled with a materialhaving a high refractive index. (This material may also change the coneangle.) However, it should be noted that light incident on the outersurface of the material filling the depressions results in specularreflection, which reduces the intensity of the retro-reflected light.

[0095]FIG. 6B shows a system similar to FIG. 4, except that it uses aretro-reflector with a cone angle of a.

[0096] In the embodiment described above, the retro-reflection has ashape that is symmetrical about a retro-reflective axis. However, asdescribed below, in some embodiments of the invention, the shape is notsymmetrical with respect to the axis. For example, the shape can beelliptical or other shapes having a 180° rotational symmetry. Asuggested utility of this type of reflection scheme is described below.

[0097] A holder, optionally a holder whose tilt and aspect isadjustable, is optionally provided to hold the card in the car or othervehicle's window. Since the positions and angles of dashboards and frontwindows are variable, it may be necessary to provide such holding andoptional adjustment to avoid situations where the aspect of a card lyingon the dashboard or stuck to the window is out of the acceptance angleof the retro-reflector.

[0098] In accordance with an embodiment of the invention, as shown inFIG. 7, card 14 is provided with a border or other marling to makeinitial identification of the card (as described below) easier. Inparticular, the card may be provided with a retro-reflecting border 50.In some embodiments, retro-reflecting border 50 is surrounded by a black(non-retro-reflecting) border 52. In some embodiments, noneretro-reflecting border 50 surrounds a black (non-retro-reflecting)border 54. In some embodiments, both retro-reflecting borders arepresent. A rectangular border of predetermined ratio of height and widthallows for secure identification of the card in an image, fordetermination of the tilt of the card (to within a half rotation) andallows for a rough calibration of the size of the card. As indicatedbelow, this may allow for more definite determination of the size of thebars in a bar code. Alternatively or additionally, other markers may bepresent to provide for secure identification of the card. For example, a“black” stripe may be placed in the center of the card in either thehorizontal (56) or vertical (58) direction, or both. If one of thestripes is off center, as shown, the tilt of the card can be determined.

[0099] In accordance with an embodiment of the invention, a code 39 barcode, in discrete symbol technology, is used as indicta. Alternatively,other symbol technologies can be used. FIG. 8 shows a card 14 havingborders 50 and 52 and a bar code 59 containing eight characters 60-67 onfour lines 68-71. In accordance with an embodiment of the invention, thespace between lines 68/69 and 70/71 is made sufficiently different sothat the difference is evident on an image acquired by camera 20. Thisallows for the removal of the 180° rotational ambiguity mentioned above.In addition, using the configuration show, no “start of scan” or “end ofscan” characters are necessary. Although a code 39 bar code is shown,other bar codes or other indicta can be used.

[0100] It is noted that a modified bar code 39, shown in FIG. 8 containstwo different characters that are each repeated three times (60, 63, 64and 61, 62, 65) and a two check-sum character (66, 67). For theconfiguration shown, two repeats of three different characters (or threerepeats of two different characters as shown) each with a duplicatecheck sum, are possible. If a higher resolution camera or shorterdistances are used, smaller characters and a larger number of characterscan be used, when the characters are repeated the modified code 39 canbe used. Alternatively, if a larger number of combinations is desired,the standard code 39 can be used without repeats.

[0101] Details of an exemplary bar code scheme are given below.

[0102] In accordance with some embodiments of the invention, the cardincludes spectral indicta. For example, the retro-reflector (or aportion thereof) may be covered with a material that passes only aportion of the spectrum of the interrogating illumination.Alternatively, the indentations are lined with a metal or other materialhaving particular spectral characteristics. In operation, the spectrumof the reflected light is measured and acts as a security measure forconfirming the authenticity of the card, or for providing morebandwidth, namely N characters for each bandwidth.

[0103] In some embodiments of the invention, two types ofretro-reflector elements are present on the surface of the card.

[0104] In an embodiment of the invention, a portion of the cardcomprises retro-reflecting elements that are close enough together tocause a diffraction pattern to be reflected. Camera 20, images thediffraction pattern. If the pattern meets a predetermined criteria, thecard is considered to be genuine.

[0105] Alternatively or additionally, the two types of retro-reflectingelements have different cone angles α and α′. As shown in FIG. 9A, twocameras 20 and 20′ are provided, one at each of the cone angles. In oneembodiment of the invention, the retro-reflecting elements areintermixed so that each portion of the image reflects light at twoangles (albeit at a reduced intensity). The presence of both images,with predetermined intensity, acts as a check on the authenticity of thecard. The images from the two images can be combined to provide for anadditional security check, since the brightness (contrast) of the imagesshould be about the same, while for a card without this feature, theintensities are very different. Alternatively or additionally, a portionof the card retro-reflects with a cone angle different from that ofanother portion. Again, two cameras are provided for acquiring theimages. The images are combined to provide a composite image from whichthe information can be extracted. The presence of both images alsoprovides a confirmation of authenticity. In an embodiment of theinvention, a border, as described above, is provided. This border mayhave both types of reflectors so that it is visible from the vantage ofboth cameras. Alternatively, two borders, one with retro-reflection ateach of the cone angles, are provided. Alternatively, only one type ofreflector is present in the border and the position of the card isdetermined using only one of the images. Further processing of the imagein the other image is based on the position determined in the firstimage.

[0106] Alternatively, a single camera can be used with combining opticsutilized to combine both images onto a single camera.

[0107] Alternatively or additionally, each of the images can comprise aseemingly random dot pattern, while the combined images (e.g., added orsubtracted) form an image.

[0108] When an elliptical or other form for the cone is provided by theretro-reflectors (as described above), and two or more cameras areprovided, for example utilizing the layout shown in FIG. 9B, the twistangle of the card can be determined. This too can act as a check on theauthenticity of the card.

[0109] Another method of authentication is shown in FIGS. 10A and 10B. Asmall laser 301 illuminates a small portion of a retro-reflector 302through a beam splitter 304. Light 305 is reflected from retro-reflector302 and, after reflection from beam splitter 304 impinges on a imagingdetector 306. This light forms an image on detector 306, which can beused to determine the conical angle α. This serves to authenticate thecard. The entire system may be contained in a hand held authenticator(as can those of FIGS. 10B-10D) indicated by a dashed line 300.

[0110] An alternative embodiment is shown in FIG. 10B In this case alens 308 focuses the light reflected from the retro-reflector. Imagingdetector 306 is placed at a predetermined position away from the focalplane of the lens, so that a ring of light is formed. If the distancesare known, the conical angle can be determined.

[0111]FIG. 10C shows an alternate authentication method, which does notrequire a laser and which can be used, at least in principle, at longerdistances since aiming of the light onto the surface is not necessary. Asmall incoherent source, such as a LED 310 is used to illuminate thecard. The beams 312 generated by the LED cause the retro-reflector toreflect conical reflected beams 314 from retro-reflector 302. Forsimplicity, the divergence of the retro-reflected beams is not shown. Itis seen that a ring of light 316 is formed around source 310 (or arounda virtual source 310′, if beam splitter 304 is used). The formation ofthe light ring is shown around the source for ease of visualization anddetector 306′ can, in fact surround the source as shown (as it can inthe embodiments of FIGS. 10A and 10B). Alternatively, it can viewretro-reflector 302 via beam splitter 304.

[0112] An alternative structure is shown in FIG. 10D. Since the ring oflight is very nearly a real image, it can be focused by a lens 318imaging the ring on the detector 306. As long as the ring angle anddistance from the retro-reflector is such that the ring of light fallswithin the diameter of the lens, this method can be used.

[0113] It should be understood that the methods of FIGS. 10C and 10Dprovide a fuzzier ring than does the laser based system, due to the factthat not all the reflections converge on the same point. However, it canstill give acceptable authentication.

[0114] It should be noted that the interrogators shown in FIGS. 10A-10Dcan be used on the same or a different portion of the card containingthe indicta, and the retro-reflector used for this authentication canhave a different conical angle than does the rest of the card. Use of aseparate portion of the card for this feature is especially useful wherethe position of the card is fixed, as with close range applications. Inaddition, sections of the card having multiple circular offset angles(using for example, the method described above) can be used. Theauthentication can then measure a more complex and harder to forgepattern. Furthermore, if a simpler detector is desired a ring of smalldetectors or a ring detector can be used as a simple go/no-go test foran authentic card.

[0115] An authentication system for cards or any other material orproduct having indicta that are not retro-reflecting can be produced bymaking a small portion of the card retro-reflecting with a particularcircular offset angle. Any of the methods illustrated in FIGS. 9A-10Dcan be used to authenticate the card. Alternatively, multiple areas canbe formed with the retro-reflecting elements having a same or differentcircular offset angle. This makes the card harder to forge.

[0116] Image Processing

[0117]FIG. 11 shows a general block diagram of a method 100 forextracting information from the indicta on card 14, in accordance withan exemplary embodiment of the invention. In general, an image isacquired by a camera (or cameras, as described in the previous sectionand in the following section) at an illumination level that allows forproper reading of the indicta and extraction of the bar codeinformation.

[0118] First, the image of the card and its surroundings is optionallypre-processed (110) to simplify the determination of information fromthe card. Next, the position and orientation of the card (if it is notin a fixed orientation) is determined (120). Next, the bar code, (orother indicta) is read (150).

[0119]FIG. 12 is a block diagram showing some detail of a preprocessingalgorithm (110), in accordance with an exemplary embodiment of theinvention. First, the resolution of the image is reduced (112), so thatthe speed of the image processing needed for determining the positionand orientation of the card is increased.

[0120] Then, the image is optionally smoothed (114) to reduce artifacts.A 2×2 or 3×3 uniform smoothing filter may be used, with the lower degreeof filtering being used when the image resolution is reduced by a factorof 3 and the higher degree of filtering being used when the imageresolution is reduced by a factor of 2. These values are representativeand are not at all critical. Non-uniform smoothing (convolution) kernelscan also be used.

[0121] Optionally, a neighborhood-maximum algorithm is applied to theimage (116). This algorithm replaces the values of pixels by the valueof a near neighbor having the highest value. This algorithm helps toreduce “holes” and non-uniformity in the image. It also substantiallyreplaces the black lines in the code by white values making thedetection of the card simpler.

[0122]FIG. 13 shows a breakdown of the acts involved in an exemplarymethod (120) for detecting the presence and position of aretro-reflecting card in the image, in accordance with an embodiment ofthe invention. First, a binary image is generated (122) at a thresholdthat will clearly differentiate the card from its surroundings. Then,the position, tilt and size of the retro-reflecting card are extracted(124) from the image. Since the aspect of the card is not generallynormal to the interrogating beam/camera, the card appears as a rhombusin the image. So also the aspect can be extracted, if desired,especially as the aspect ratio of the card is known.

[0123] Once the position and orientation of the image of the card aredetermined, the method reverts (126) to the originally acquired imagefor the rest of the algorithm. Optionally, image is “coarse cut” (128)to orient the card in Cartesian coordinates (taking note of the factthat the card may not appear rectangular) and removing the portions ofthe image that are not associated with the card itself. In someembodiments of the invention, the image is warped to fit a rectangle ofthe known width to height ratio. Then, the exact horizontal and verticalposition of the card is determined (130). This determination is aided byaforementioned borders 50 and 52. In the absence of such borders, whichare optional, the exact extent of the card can be determined from thetransition between the very bright edge of the card and the relativelymuch darker background.

[0124] The rest of the image (other than the card itself) may besubstantially black if, for example, the illumination is pulsed and theshutter of the camera is synchronized with the illumination. In somecases, is desirable to have some information about the surroundings ofthe card. In such cases, the rest of the image is “gray”. In general,the algorithms given below are capable of extracting the position andorientation of the card from the background of a gray image.

[0125] The grayness of the image can be removed and the contrast of theimage enhanced, in accordance with an embodiment of the invention, byacquiring, in addition to the retro-reflected image a second image, animage at a non-retro angle (hereinafter a “background” image).Preferably, the images are acquired at the same wavelength. Theadditional image is very similar the main image, except that theretro-reflected indicta and background is not present. The backgroundimage is subtracted from the main image, which leaves only the effectsof retro-reflected portion of the image. This subtracted image can beused for either or both determination of the position and orientationand the reading of the bar code. An edge removing filter can be usedafter this operation to remove lines created by the slightly differentangle of viewing.

[0126] The image of the card is then “scanned” to determine thepositions (132) of the bar codes (hereinafter “stacks”) and the spacesbetween the bar codes. Optionally, this is done by determining theaverage intensity for each of the lines of pixels along the largerdimension of the card. The lines with bar coding will have a much loweraverage intensity. As indicated above, when the spacing between thelines is not the same, the different spacing measurements allows for thedetermination of which side is the “up” side of the card. Alternatively,the up side of the card can be determined after the card is read, butbefore decoding of the information. Additionally or alternatively,spaces between characters are different on the two outermost rows. Thetop and bottom of the card can be determined from these spacings.

[0127] Other markers (such as circles in predetermined positions) canalso be used to orient the cards.

[0128]FIG. 14 is a summary flow chart of an exemplary algorithm (150)for reading bar code 59 on card 14, in accordance with an embodiment ofthe invention.

[0129] In accordance with some embodiments of the invention, one or morepre-processing functions are applied (160) to the image prior toreading. In accordance with some embodiments, a bar code is read usingmore than one set of parameters (180). The “best” result is then chosen(190) using one or more criteria.

[0130]FIG. 15 is a more detailed flow chart of pre-processing of theimage, in accordance with an exemplary embodiment of the invention(160).

[0131] The image is also optionally noise-reduced (162), for example,using a median filter, since this filter does not substantially changethe resolution of the image. The size of the kernel for the medianfilter is determined based on the width of the narrow lines of the code,as estimated by the size of the image of the card. Generally, the kernelsize should be slightly smaller than the width of the line. This mayimprove the image for reading. Sometimes, however, it makes it worse.The reading of the data may be performed on each of the noise reducedand unprocessed images (each of which is further converted into rows ofdata as described in the following paragraph).

[0132] The stacks are converted into rows of data (164). Several methodsmay be employed, and, in some embodiments, more than one of these istested (as for example at 180 of FIG. 14). One variation present inthese methods is basing the data row on different parts of the stackheight (i.e., the long dimension of the bar). For example, data rows maybe generated based on the integral of the intensity along the height ofthe stack. Other sets of row data are generated, for example, using thetop, bottom or middle 10% of the bar height (each conveniently about 1pixel high) or on the integral over the middle 50% of the height of thestack. Utilizing a number of different portions of the stack isdesirable, especially in the presence of noise, blurring, glare,obstruction or other localized interference. Generally, if noisereduction is also performed, eight candidate data sets are generated.Alternative rows of data may be generated by reading from right to leftas well as from left to right. The code starts from a white area.Rarely, the image is not cut correctly and the reading from one sidegives an incorrect result, while the reading from the other end iscorrect.

[0133] The rows of data are then binarized (166). Due to the largevariations in intensity that are possible in actual situations, theapplication of a fixed threshold for determining the transition fromblack to white lines is generally, but not always inappropriate. In someembodiments of the invention, the values of intensity on the bar codeportion of the image are normalized using the intensity values on thebright and dark border portions of the image. These can be used toreduce the effect of global intensity parameters such as glare, weather,illumination variations and aspect angle. Various methods for flatteningthe background, as known in the art of image processing, may also beused.

[0134] In accordance with an embodiment of the invention, binarizationcomprises two parts. The first of these is the determination of thelocal extrema of the row of data (168). Extrema (a minimum, for example)may be determined by comparing the value of each element in the row ofdata with the next element. The maximum (for instance) is defined as thefirst point where the value is larger than the next point, and largerthan a statistical value determined from the gray levels of the code.

[0135] Similar criteria apply for determining relative minimum.

[0136] After determining the local minima and maxima, a local threshold,for the range between a particular minimum and maximum is set (170) halfway between the adjacent minimum and maximum. The row of data is thenbinarized using this threshold. Other methods of determining a thresholdcan be used, for example, using a local threshold between every two barsin a character rather than a same threshold for the entire line.

[0137]FIG. 16 is a general flow chart of an exemplary method (180) ofreading of the bar code, in accordance with an embodiment of theinvention. This method includes two main portions, adjusting the widths(182), setting a threshold for wide and narrow lines (184) and adjustingthe threshold until a “good” code, i.e., one that meets criteria for acode 39s, is achieved (186).

[0138] As to adjusting the widths (182), in an embodiment of theinvention, after the widths are found, the widths are adjusted based onthe “energy” (i.e. the integral of the intensity difference from acentral value) in each bar. For example, in some situations, blurringmay not be uniform across the field of view, or different bars bay bedifferently situated with respect to the pixels. Under such conditions,the some bars may appear to be wider or narrower than others. However,widening the bars causes a decrease in the intensity of the pixels.However, the energy is substantially conserved. Thus, the energy can beused to correct the measured width, for example, when the energy islower than a normative value, the width is reduce. Alternatively, theenergy itself can be used to define the width of the bars.

[0139] Empirically, a bar situated between two wide bars is imaged asbeing wider than it actually is, especially if blurring exists. In anembodiment of the invention, the width of a bar is reduced by one pixel,if it is situated between two wide bars. It is understood that thesecorrections are empirical and may not be necessary in some practicalembodiments of the invention. Furthermore, other empirical correctionsmay be necessary. Alternatively or additionally, the system may becalibrated to recognize and adjust the values of some standard patterns.

[0140] The determination of whether a line is wide or narrow isdetermined by arranging the widths of the nine elements in the characterin order of length. Each set has three wide bars and six narrow bars, sothat the three widest bars are determined to be wide and the other sixare determined to be narrow.

[0141] The “best” decode is chosen. First invalid groups (those withmore than or fewer than 9 lines, for example) are rejected. The bestdecode may be defined as the most common character (among the multipleoutputs that correspond to the same physical character). In addition analternate code is chosen, namely, the second most common code, where atleast two codes have the same output value.

[0142] Since characters are repeated, the actual character value ischosen as the value that appears the most times, among the best code andalternate codes for all of the repeats of the character.

[0143] It is clear that, in some embodiments of the invention, othermethods of determining a best choice of character can be used.

[0144] It will be clear that the present application describes a numberof different elements, including, inter alia a card having one ofseveral novel retro-reflectors, a novel code, novel methods ofdetermining the position and orientation of a target, such as a card,novel methods of reading a code, novel apparatus for acquiring images ofa card and various security measures that are novel. It should be clearthat many of these novel elements can be utilized, in some embodimentsof the invention, without any of (and certainly without all of) theothers.

[0145] For one example, the reader is referred to FIG. 17, in which astandard type retro-reflector is used, in which there is no offsetangle. A code, as described above may optionally be used. A beamsplitter 304′ may be used to direct the reflected beam to camera 20.Optionally, the source produces linearly polarized light. A quarter waveplate is placed on the indicta, so that no light is returned to thesource from the retro-reflector.

[0146] Furthermore, while the invention has been explained in detail,mainly in the context of a card for distance viewing in a vehicle,objects utilizing one or more aspects or features of the presentinvention can also be utilized for credit card, smart cards, EM smartcards, personal access control card. The present invention is alsoapplicable to authentication labels for products, for stock control andfor any other uses for which cards and stickers are used. While theinvention is described for use with a card, the form of theretro-reflector can be a sticker, (either rigid or flexible) or can beformed directly on any other surface.

[0147] Furthermore, while the card has been described with thecharacters stacked two to a stack in rows that are parallel to the longside of the card, the characters may be stacked in the direction of thelong side such that the characters run in a direction parallel to theshort end. Furthermore, while the invention has been illustratedutilizing a modified code 39, an unmodified code 39, two dimensionalcodes and other forms of indicta may be formed on the cards and read, inaccordance with various embodiments of the invention.

[0148] An appendix attached to a US Provisional application entitledELECTRO-OPTIC READERS and filed on the same day as the present PCTapplication contains source code for performing the image processingpart of the present invention. This provisional application isincorporated herein by reference.

[0149] It will thus be clear, the present invention has been describedusing non-limiting detailed descriptions of exemplary embodimentsthereof that are provided by way of example and that are not intended tolimit the scope of the invention. Variations of embodiments of theinvention, including combinations of features from the variousembodiments will occur to persons of the art. The scope of the inventionis thus limited only by the scope of the claims. Furthermore, to avoidany question regarding the scope of the claims, where the terms“comprise,” “comprising,” “include,” “including” or the like are used inthe claims, they mean “including but not necessarily limited to”.

1. A system for identification comprising: a surface comprisingretro-reflective indicta; a source of light that illuminates the indictaalong an illumination direction; and a detector that views lightreflected from the indicta, wherein the retro-reflector reflects thelight that illuminates it as a plurality of beams at a plurality ofangles relative to the illumination direction.
 2. (Canceled)
 3. A systemaccording to claim 1 wherein the plurality of beams lie on the surfaceof a circular or elliptical cone.
 4. (Canceled)
 5. A system according toclaim 1 wherein the plurality of beams provide a substantiallycontinuous ring of reflected light.
 6. A system according to claim 5wherein the ring of light has substantially of the same intensity alongits length.
 7. A system according to claim 1 wherein the source anddetector illuminate and view the surface at angles having a differencesubstantially equal to at least one of the multiple reflection angles.8. (Canceled)
 9. A system according to claim 1 wherein the plurality ofbeams define the surface of two or more cones. 10-14. (Canceled)
 15. Asystem according to claim 7, wherein the detector is an imagingdetector, that forms an image of the light retro-reflected from thesurface.
 16. (Canceled)
 17. A system according to claim 15 wherein thesource of light does not scan the surface.
 18. A system according toclaim 15, wherein the imaging detector images a field of view that hasan area at least 5 times as large as the area of the surface.
 19. Asystem according to claim 18 wherein the imaging detector images a fieldof view that has an area at least 20 times as large as the area of thesurface.
 20. (Canceled)
 21. A system according to claim 19 wherein theimaging detector images a field of view that has an area at least 100times as large as the area of the surface.
 22. A system according toclaim 15 and including an image processor that detects the presence ofthe surface in an image acquired by the imaging detector, wherein theretro-reflecting surface reflects light that forms an informationcarrying image and wherein the image processing circuitry is operativeto extract the information from the image.
 23. (Canceled)
 24. A systemaccording to claim 22 wherein the information comprises a bar code. 25.A system according to claim 22 wherein the information comprises a twodimensional code.
 26. A system according to claim 22 wherein theinformation comprises spectral information.
 27. A system according toclaim 1 wherein the source of light illuminates the surface withincoherent light.
 28. A system according to claim 1, wherein the sourceand detector illuminate and view the surface at substantially the sameangle.
 29. A system according to claim 28, wherein the detector is animaging detector.
 30. A system according to claim 29 wherein the imageon the imaging detector comprises a pattern corresponding to the anglesat which the light is reflected.
 31. A system according to claim 28 andincluding authentication circuitry which authenticates the surface whenthe detector detects a predetermined pattern of light.
 32. A systemaccording to claim 28 and including a reflector that reflects the lightreflected by the retro-reflector so that it can be viewed outside thepath of illumination.
 33. (Canceled)
 34. A system according to claim 33claim 32 wherein the detector is situated at the plane of the source orat a virtual plane of the source or at an image of said source plane orvirtual source plane.
 35. (Canceled)
 36. A system according to claim 28wherein the light source is a laser.
 37. A system according to claim 36wherein the detector views the light reflected by the retro-reflectorwithout any focusing of the reflected light.
 38. A system according toclaim 35 or claim 36 and including a focusing element, having a focallength, that receives the light reflected by the retro-reflector,wherein the detector is placed in the path of the thus reflected beam,spaced from the focusing element by a distance other than the focallength. 39-43. (Canceled)
 44. A retro-reflective surface havinginformation encoded thereon by having different areas thereofretro-reflecting with different retro-reflective intensities, to formindicta carrying the information, wherein the retro-reflector reflectsthe light that illuminates it as a plurality of beams at a plurality ofangles to the illumination direction.
 45. A surface according to claim44 wherein the plurality of beams lie on the surface of a circular orelliptical cone.
 46. (Canceled)
 47. A surface according to claim 44wherein the plurality of beams provide a substantially continuous ringof reflected light when illuminated by a beam of light. 48-52.(Canceled)
 53. A surface according to claim 44 wherein the informationis comprised in a two-dimensional code.
 54. A surface according to claim44 wherein the information is comprised in a bar code.
 55. A surfaceaccording to claim 54 wherein the bar code is a stacked one-dimensionaltype code. 56-61. (Canceled)
 62. A surface according to claim 44 whereinthe plurality of beams define the surface of two or more circular orelliptical cones. 63-70. (Canceled)
 71. A method of reading a bar codecomprising: forming an image of a bar code, having at least 8 symbolswith a camera from a distance of more than 10 meters; and determiningthe symbols represented by the bar code.
 72. (Canceled)
 73. A method ofreading a bar code comprising: forming an image of a bar code with acamera from a distance of more than 10 meters; and determining thesymbols represented by the bar code, wherein the bar code is comprisedin a retro-reflected image and including illuminating the bar code withlight from a controllable light source: and wherein the retro-reflectedimage is reflected with a offset angle relative to the angle ofincidence of the illumination from the light source.
 74. A methodaccording to claim 73 wherein the distance is more than 15 meters.
 75. Amethod according to claim 73 wherein the distance is more than 20meters.
 76. A method according to claim 73 wherein the distance is morethan 25 meters.
 77. A method according to claim 73 wherein the bar codeis formed on a credit card sized substrate.
 78. A method according toclaim 77 wherein the bar code includes at least 8 symbols.
 79. A systemaccording to claim 9, wherein the detector is an imaging detector, thatforms an image of the light retro-reflected from the surface.
 80. Asystem according to claim 79 wherein the source of light does not scanthe surface.
 81. A system according to claim 79, wherein the imagingdetector images a field of view that has an area at least 5 times aslarge as the area of the surface.
 82. A system according to claim 79wherein the imaging detector images a field of view that has an area atleast 100 times as large as the area of the surface.
 83. A systemaccording to claim 79 and including an image processor that detects thepresence of the surface in an image acquired by the imaging detector,wherein the retro-reflecting surface reflects light that forms aninformation carrying image and wherein the image processing circuitry isoperative to extract the information from the image.